Conventionally austenitic heat-resisting cast steel has been used for the components of an exhaust system in an automobile, such as an exhaust manifold and a turbine housing. Such components are used in severe environment at high temperatures. For excellent thermal fatigue resistance, they are required to have excellent high-temperature strength and such toughness from room temperatures to high temperatures.
In this respect, Patent Literature 1, for example, proposes austenitic heat-resisting cast steel containing 0.2 to 0.6 mass % of C, 0.1 to 2 mass % of Si 0.1 to 2 mass % of Mn, 0.05 to 0.2 mass % of 5, 0.05 mass % or less of Se, 10.0 to 45.0 mass % of Ni, 15.0 to 30.0 mass % of Cr, 8.0 mass % or less of W, and 3.0 mass % or less of Nb, and iron and inevitable impurity as a remainder, and includes an austenite phase mainly containing Fe—Ni—Cr as the parent phase.
For better heat resistance, this austenitic heat-resisting cast steel includes C, Ni, Cr, W, and Nb added. For better machinability, this heat-resisting cast steel includes Mn and S to generate free-cutting particles of MnS. This heat-resisting cast steel includes a free-cutting element Se added for much better machinability.